More whales have been spotted in San Francisco Bay than usual, and scientists are concerned that it could be a sign of starvation.

When they’re hungry, they can’t complete the full migration from California to Alaska, where they spend the summer. They stop longer during the trek in hopes of finding food to fuel their journey.

A few of the dead whales have shown serious signs of emaciation. Others were likely killed by ship strikes, which could be an indirect result of them staying in heavily congested San Francisco Bay for longer periods than usual.

Research biologist John Calambokidis said a potential cause for the starving animals could be a boost in the gray whale population, which would mean be less food to support them all. But he also believes climate change could be a factor. Weather shifts in the Arctic, including water temperature and ice cover, could be weakening the whales’ food supply.

Gray whales, which have a life expectancy of 55 to 70 years, usually grow up to 50 feet long and weigh about 40 tons.